In-well air stripping, oxidation, and adsorption

ABSTRACT

A method and system for removing contaminants for the phreatic zone, also known as the saturation zone, or groundwater. The technique involves gas sparging and oxidation while increasing the surface area for mass transfer by the placing of packing balls into the eductor tube. The system is comprised of a means for supplying gas/ozone mixture to the lower extent of a well which induces a flow of groundwater and gas bubbles up the well. The system contains a conduit within the well, which extends below the water table The conduit has a lower fluid-permeable section which is located below the water table and an upper fluid-permeable section which is adjacent the water table.

This is a continuation of U.S. application Ser. No. 08/858,267, filedMay 19, 1997 now U.S. Pat. No. 6,007,274.

BACKGROUND OF THE INVENTION

The present invention relates generally to a method and apparatus forremoving contaminants from groundwater, and, more particularly to anin-situ air stripping, oxidation, and adsorption method for removingvolatile organic compounds (VOCs) from groundwater.

Contamination of the phreatic zone, also known as zone of saturation,or, groundwater, with potentially hazardous materials is a commonproblem facing industry, the government and the general public. The mostcommon type of VOC pollutants are petroleum based products andchlorinated solvents. Frequently, as a result of spills, leakage fromstorage facilities or surface discharges, contaminants percolate intogroundwater, thereby posing a threat to drinking water supplies.

While groundwater is not as susceptible to pollution as surface water,once polluted, its restoration is difficult and long term. Typically,contaminated groundwater is removed from the phreatic zone, treated anddischarged or returned to the phreatic zone. These "pump-and-treat", orabove ground, methods, are relatively expensive. There have been somerecent developments in insitu water treatment which employ air liftpumping as a means of producing gas bubbles to remove VOCs. The theoryof these known methods is that gas is pumped into the wells which causeswater and subsequently formed gas bubbles to rise upward. VOCs aretransferred from the contaminated water to the gas bubbles which canthen be collected for treatment. However, frequently these devices donot result in rapid mass transfer and vapor saturation which results ina slower and less efficient process. Vapor saturation occurs when therising bubbles become saturated with VOC vapor. Therefore, there is aneed for the development of an insitu air stripping, oxidation, andadsorption remediation method for removing contaminants in a relativelyinexpensive and more efficient manner.

The present invention involves new concepts for in-well removal ofcontaminants from the saturation zone. It avoids expensive "aboveground" remediation methods, and provides a more efficient method ofmass removal of dissolved contaminants. The present invention combinespacking/stripping materials (balls) with air stripping techniques in thewell. In addition oxidation and adsorption techniques can also beincorporated to compliment the air stripping effect to achieve highermass removal efficiencies. The injected gas may be air or any specificor combination of gases such as nitrogen gas. The injected gas can be atany desired temperature.

SUMMARY OF THE INVENTION

Objects of the invention, as will be apparent herein, are accomplishedby injecting a gas into the lower extent of a well to force groundwaterup the well through air lifting, causing VOCs to be transferred torising gas bubbles inside the well. The available surface area forcontaminant mass transfer within the flow of the mixture of groundwaterand gas bubbles is increased by placing packing balls (preferably JAEGERTRIPACK packing material) into the well. This step significantlyincreases the overall mass transfer efficiency of this device. The gasbubbles, containing VOC vapors are then separated from the groundwaterat the upper extent of the well. As this process is repeated and thegroundwater continues to circulate, the VOC concentrations in the waterare reduced. In addition ozone can be mixed with the injected gas toenhance the mass removal by direct oxidation of the contaminantspresent.

It is preferable that the air be supplied to the lower extent of thewell by operating an air pump which is in fluid communication with atube positioned in the well in a conduit, where the tube has an openingat its lower extent. Ozone can be added to this line of injection.

It is also preferable that the separated gas bubbles and captured air bestored upon being released from the conduit. It is also preferable thatthe contaminants be removed from the captured air prior to discharge tothe atmosphere.

The system for removing VOCs from contaminated groundwater is comprisedof a means for supplying gas and ozone to the lower extent of a wellwhich induces a flow of groundwater and gas bubbles up the well. Thesystem contains a conduit within the well, which extends below the watertable The conduit has a lower fluid-permeable section which is locatedbelow the water table and an upper fluid-permeable section which isadjacent the water table. The present invention is further comprised ofan internal pipe or eductor tube contained in the conduit which extendsfrom the top extent of the conduit to the saturation zone. Packingmaterials are located between the eductor tube and the means forsupplying gas to the lower extent of the well to increase the availablesurface area for mass transfer. The present invention also contains ameans, which is located near the top of the conduit, for separating thegas bubbles from the groundwater.

It is preferable that the system of the present invention contain a gassupplying means which includes a tube contained within the conduit andeductor tube, which extends from above the ground surface to below thewater table, a pump which supplies air to the tube and an ozonegenerator to provide the right amount of ozone.

It is also preferable that the system of the present invention contain abentonite seal located between said conduit and well wall to separatethe treated clean water from the contaminated water.

It is preferable that the system of the present invention contain ameans for capturing the gas bubbles which have been separated from thegroundwater.

Objects and advantages of the present invention will be readily apparentupon a reading of the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred method and system herein described are not intended to beexhaustive or to limit the invention to the precise forms disclosed.They are chosen and described to explain the principles of theinvention, and the application of the method to practical uses, so thatothers skilled in the art may practice the invention.

As shown in FIG. 1, the present invention removes VOCs from contaminatedgroundwater by supplying a gas such as air and ozone mixture into a well18. When air/ozone mixture is injected into a well, groundwater islifted upward through the well creating a recirculating cleaningprocess. As the groundwater rises up through the well, VOCs aretransferred from the contaminated groundwater to rising air bubblescreated by the air supply in addition to direct oxidation by ozone. TheVOC vapor is then released at the top of the well or, alternativelycaptured for treatment. The treated water, which is now free of aportion of VOCs, flows out of the conduit 16 to mix with thegroundwater.

FIG. 1 illustrates one embodiment of the present invention. A borehole12 is positioned in the contaminated area extending down into thephreatic, or saturated, zone 14 of the well 18. The external conduit 16is positioned within the borehole 12. The conduit 16 has twofluid-permeable sections: one located near the base of the conduit at 20below the water table and the other 21 located near the water table 22,but below ground level 24. The fluid-permeable sections may be comprisedof screened PVC pipe or another suitable material. The remainingportions of conduit 16 may be comprised of impermeable material such asPVC pipe or another suitable material.

An internal pipe 30, or eductor pipe, is placed between the air tube 26and the external pipe 16. The air being pumped into the well iscontained in the eductor pipe. The eductor pipe 30 may also be closed atthe lower end. If the eductor pipe is closed at the lower end, slotsplaced at the lower end can allow water to flow into the pipe whilepreventing air bubbles from escaping.

A compressed air tube 26 is positioned within the conduit 16 and extendssubstantially to the base of the conduit 16 at 28. The tube 26 may beopen at the base at 26 and attached to an air pump 29 and an ozonegenerator 54 at the top of the conduit. Alternatively, an air pump maybe located at the base of the conduit 16 and connected to tube 26 at 28(not shown). A packer 56 may be placed inside the well.

The operation of the present invention may be understood by reference toFIG. 1. Groundwater may flow through the phreatic zone 14 as illustratedby the solid line arrows 38. Alternatively, the groundwater may not flowthrough the phreatic zone. The present invention operates effectively ineither case.

An air pump is operated to force air into the air tube 26 down to thebase of the conduit 16 at 28. A gas, such as carbon monoxide, can alsobe used as appropriate. The air can be injected at various rates to varythe rate at which groundwater circulates toward the well.

The air/ozone mixture, being pumped into the tube, is released at thebase of the conduit 28, creating air bubbles and introducing ozonemolecules. Subsequently, water flows up the well, while watersurrounding the well is pulled towards the well. The water/air mixturerises up in the space, or "mixing zone" 40, between the air tube 26 andthe eductor tube 30. As the air rises, it mixes with the water withinthe eductor tube and creates water flow from the lower permeable section20 of the conduit 16 upwards through the conduit and out of the upperpermeable section of the conduit 21.

During the time that the water/air mixture is flowing up the eductorpipe, VOCs are transferred from the water to the gas phase in additionto oxidation of contaminants to inert end products. Or in other words,while mixing with the water, the air strips the water of volatilecontaminants in the mixing zone 40 in addition to direct oxidation. Theair/contaminant gas mixture is then separated from the water/air mixturenear the top of the conduit 16. Once the gas is separated from thewater, the gas mixture is then released above the water table into theatmosphere. Alternatively, the air/contaminant gas mixture may becaptured for treatment or discharge. The VOC vapor can be extracted fromthe gas mixture using vacuum vapor extraction techniques also to enhancethe stripping efficiencies of contaminants. Once the air is separatedfrom the water, the water, less a portion of VOCs, is passed back intothe aquifer through the upper permeable section 21 of the conduit 16.

As discussed previously, while the water/air mixture is flowing up theeductor pipe, VOCs are transferred from the water to the gas phase inaddition to oxidation of compounds. However, frequently this processdoes not result in complete mass transfer of the contaminants. Massremoval occurs when the rising bubbles become saturated with VOC vaporin addition to the oxidation. When incomplete stripping occurs, smallamounts of VOCs are left in the effluent water. This results in a poorstripping efficiency which results in a slower and less efficient cleanup process. To enhance the stripping process, packing materials such asJAEGER TRIPACK packing balls 42 are placed in the zone 40 to cause theair and water to pass over the surface of the balls resulting in a moreefficient air stripping. Several different packing materials may be usedto achieve a similar result to the preferred JAEGER TRIPACK packingballs.

Adsorption media 50 may be placed in a trench 52 or annular holes nearthe top of the well for use in remediating residue of contamination notremoved by the air stripping and/or contaminants, such as heavy metals,which are not removed by air stripping or oxidation by ozone. As thewater and vapor leave the screened portion 21 of the well, in thepreferred embodiment it must pass through the adsorption media 50 thatresides in the trench 52. An example of an adsorption media is activatedcarbon or ion exchange material.

What is claimed is:
 1. A method for removing contaminants fromgroundwater, comprising:providing a well extending from the groundsurface into the saturated zone; providing a conduit within the well,extending below the water table, the conduit having a lowerfluid-permeable section below the water table and an upperfluid-permeable section adjacent the water table; injecting a gas intothe lower extent of the well to induce a flow of groundwater and gasbubbles up the well; providing packing material in the conduit so thatthe groundwater and gas bubbles flow over a surface of the packingmaterial causing volatile organic compounds (VOCs) to be transferred torising gas bubbles; and optionally separating the gas bubbles from thegroundwater.
 2. The method of claim 1 further comprising treating thegas bubbles to remove contaminants.